Definition: byte order

The order of numbers in a computer word. Byte order refers to the order of digits in computer words at least 16 bits long. See word.

Big Endian and Little Endian
Big endian is how we normally deal with numbers: the most significant byte or digits are placed leftmost in the structure (the big end). Known as the "network byte order," the TCP/IP Internet protocol also uses big endian regardless of the hardware at either end.

Some CPUs, most notably x86 CPUs, deal with words in little endian order, which places the least significant digits on the left (the little end). Since numbers are calculated by the CPU starting with the least significant digits, little endian numbers are already set up in the required processing order.

Bi-Endian
A bi-endian machine, such as ARM and PowerPC, supports both big endian and little endian words. In the following example, the decimal number 450 is shown in both byte orders in hexadecimal notation, which is 01C2. See hex.

 HEX NUMBER 01C2

 Big Endian (BE)   Little Endian (LE)

 01C2              C201


 CPU EXAMPLES

 Big Endian        Little Endian
 Motorola 68K      x86 (Intel, AMD, etc.)
 IBM mainframes    PDP-11, VAX

 Bi-Endian
 ARM
 PowerPC
 Itanium

Choosing Byte Order for TIFF Images

TIFF images store pixel values as words, and their byte order was not the same when Windows and Mac used different CPUs. This Photoshop dialog box asks which platform the TIFF file is saved on. GIFs and JPEGs are not word oriented, and byte order does not matter.